text: Housekeeping genes account for majority of the active genes in the genome, and their expression is obviously vital to survival. The housekeeping gene expression levels are fine-tuned to meet the metabolic requirements in various tissues. Biochemical studies on transcription initiation of the housekeeping gene promoters have been difficult, partly due to the less-characterized promoter motifs and transcription initiation process.
  Human housekeeping gene promoters are generally depleted of TATA-box, have high GC content and high incidence of CpG Islands. In Drosophila, where promoter specific CpG Islands are absent, housekeeping gene promoters contain DNA elements like DRE, E-box or DPE. Transcription start sites of housekeeping genes can span over a region of around 100 bp whereas transcription start sites of developmentally regulated genes are usually focused in a narrow region. Little is known about how the dispersed transcription initiation of housekeeping gene is established. There are transcription factors that are specifically enriched on and regulate housekeeping gene promoters. Furthermore, housekeeping promoters are regulated by housekeeping enhancers but not developmentally regulated enhancers.